For more than 200 years, British ministers have sat at a long, oak table in 10 Downing Street, in a room lit by three brass chandeliers. History hangs heavily inside its walls. Looking out onto a rose garden, the Cabinet Room, in the shape it is seen today by ministers and officials, was finished in the late 1700s, just in time for the 1798 Rising.

In the centuries of debate that have taken place around the Cabinet table since, Ireland has frequently dominated: famine, rebellions, independence, two world wars.

For nearly 40 years, the Troubles consumed attention. In 1993, the room was itself nearly destroyed when an IRA mortar-bomb exploded in the garden just metres away.

Leaving the room together during the Anglo-Irish Treaty talks in 1921, FE Smith, Lord Birkenhead, said to Michael Collins: “I may have signed my political death warrant tonight.”

Collins, who would die within the year at Béal na mBláth, turned to Birkenhead and, in words that have resonated through the decades, said: “I may have signed my actual death warrant.”

On March 12th, Enda Kenny passed the four Corinthian columns that mark the entrance to the room to meet with British prime minister David Cameron, surrounded by nearly 40 ministers and officials.

It was an encounter that lacked the grand historical moment and it was the better for it.

Even in recent decades, such encounters between taoisigh and prime ministers would have been rare. When they did happen they would have been inevitably been dominated by Northern Ireland.

Last month, problems with plans to harvest wind energy from the Irish Midlands and sell it into the UK’s national grid featured high – an issue potentially worth billions but not one of life or death.

The thawing of British/Irish relations has been a long time in gestation; beginning in the early 1970s, perhaps when both joined the club that was to become the European Union.

Frequently, Ireland and Britain shared common interests, over trade, for example and in their preference for a lighter-touch regulation than Continental colleagues would have liked.

Certainly, there have been disagreements. The Irish have for years tucked in behind the French to defend the Common Agricultural Policy – a pet-hate of most British politicians and civil servants.

Nevertheless, the experience of agreement, where it has occurred, has helped to deepen relations – a point that explains the Irish fervour in wanting the UK to remain in the EU.

Meanwhile, decades of engagement about Northern Ireland – despite all of the arguments and temper-filled nights– helped to cement ties, even during some of the darkest hours.

So, too, have unsung bodies such as the British-Irish Association, which brought together politicians but – just as importantly, if not more so – officials, helping to break barriers between them.

Equally, Ireland’s economic growth has made it important to some in Britain in a way it never was when, to put it bluntly, the only exports of note were cattle and people.

In recent years, Irish diplomats in London, such as David Cooney, Bobby McDonagh and now Dan Mulhall, have taken every opportunity to drive home Ireland’s significance.

Each time it happens, as it did at a St Patrick’s Day celebration in the embassy this year, British audiences react with surprise when told that Ireland is the UK’s fifth largest export market.

“Britain sells more to Ireland than to China, India and Brazil combined: that is 5.5 per cent of everything that Britain sells abroad,” Mulhall told his guests last month. It never fails to impress.

In January, British defence secretary Stephen Hammond stood with Irish Enterprise Minister Richard Bruton under a joint banner at an aviation trade event in Singapore.

The sight, unthinkable just a few years ago, fulfils one of the hopes of the much-vaunted agreement signed between Kenny and Cameron in Downing Street last year.

The two leaders, by putting trade, business and jobs at the core of the new relationship, are prepared to co-operate where it makes sense, even if there are areas where it does not.

For instance, both the Department of Agriculture in Dublin and its British equivalent, the Department of Environment, Food and Rural Affairs, are opposed to a combined pitch to the world on farming.

The wind-energy deal, meanwhile, has brought British officials and ministers into a new world of talks with their Irish counterparts, even though it has had its troubles.

For now, it is not clear that those difficulties can be overcome. Last month, Kenny and Cameron instructed that one more attempt be made but the plan arouses strong sentiments in the Midlands.

Nevertheless, economic co-operation offers both the chance to learn: the Irish can benefit from the UK’s scale, while Enterprise Ireland’s hand-holding of high-potential start-ups has impressed in London.

Meanwhile, Irish Department of Justice officials are now used to making fortnightly visits to London as the countries’ visa and immigration systems become increasingly intermeshed.

Under the Common Travel Area, Ireland has never been classified as “foreign” by the British authorities, though in an increasingly globalised world that requires co-operation to sustain it.

Later this year, a one-stop visa for Ireland and the UK should be ready to cover Indian and Chinese tourists and, even more importantly, business-people.

Meanwhile, the most senior Irish and British civil servants – secretaries-general on the Irish side, permanent secretaries on the other – meet annually.

The latter encounter is still bedding in but the possibilities for co-operation that could flow from it in the years ahead are high.

However, there is much to do. The Conservative/Liberal Democrat coalition has never regarded Northern Ireland as a priority, preferring to keep it out of Number 10, if possible.

Cameron’s determination not to become embroiled is logical, in part – since he argues that devolved political institutions, such as Stormont, should govern where they are supposed to do so.

On occasion, however, the lack of “touch and feel” has been evident, even if Cameron did quickly neuter Peter Robinson’s threat to quit as First Minister over the “on-the-runs” controversy.

Equally, the focus on the relationship on the east/west relationships – “Strand Three” talks, to a generation of Northern Ireland peace-process watchers – is greater in Dublin than it is in London.

There, ministers have understood the importance of the economic numbers, but few could travel far beyond the briefing note handed out by the Treasury on such occasions.

Equally, there has been little increase among them in curiosity about Ireland beyond the numbers – understandable, perhaps, but a subject that would repay investment on both sides.

Economically, politically and socially, Ireland and Britain have never been closer – a relationship that was encapsulated in a rugby match that took place in Croke Park in 2007 and by a monarch’s visit four years after that.

However, this is a journey that – to borrow Winston Churchill’s words from another time, another place – is, perhaps, not at the beginning of the end but, rather, the end of the beginning.

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